Are there any Windows IDEs that support both Ruby and Python?
I'm talking about the type of IDE that has syntax suggestions (auto-completion feature).
I've tried Netbeans but it only seems to support Ruby (maybe there's a way to add Python support?)

I concur with the views on NetBeans, the Ruby support is very good, but Python is still in its early stages, and has one or two annoying bugs. Still, the basis is there for a truely excellent free Python IDE. A nice alternative is Aptana Studio, which is based on Eclipse, but overall more stable and user-friendly, in my experience. It has support for Ruby on Rails built-in, and also Python through the excellent PyDev plugin.

I use Komodo IDE ( licensed version ). Its got language support for PHP/Python/Ruby and also some code assistance for popular frameworks like Rails/Cakephp/Pylons. Plus you can make macro's to run individual support libraries like baking controller/model's with a input from a input box.

Netbeans 6.5 has build in Ruby & RoR support, and includes Python support. Aptana, a version of Eclipse supports both Ruby/RoR & Python. You can also install these as plug-ins to a default Eclipse install.

I've looked into this recently as well, and both netbeans and eclipse have rudimentary python support. For whatever reason, ruby seems to have better support in these tools. If you don't mind a seperate IDE for python, you might take a look at IronPython Studio. IronPython is a .net implementation of Python, and the IronPython Studio is a Visual Studio style IDE for IronPython. I haven't used it much, but it is certainly interesting.

I've played with more editors than I can count, but I always keep coming back to SlickEdit. Powerful, fast, easy to use, hugely customizable, does dynamic auto-completion and (apparently) it even has a python debugger!